1. Field
The present disclosure relates generally to energy transfer elements and, more specifically, to energy transfer elements utilized with power converters.
2. Discussion of the Related Art
Many electrical devices, such as cell phones, personal digital assistants (PDA's), laptops, etc., utilize power to operate. Because power is generally delivered through a wall socket as high voltage alternating current (ac), a device, typically referred to as a power converter, can be utilized to transform the high voltage ac input to a well regulated direct current (dc) output through an energy transfer element. Switched mode power converters are commonly used due to their high efficiency, small size, and low weight to power many of today's electronics. In operation, a switch is utilized to provide the desired output quantity by varying the duty cycle (typically the ratio of the on-time of the switch to the total switching period), varying the switching frequency, or varying the number of pulses per unit time of the switch in a power converter. A controller may be utilized to provide output regulation by sensing and controlling the output in a closed loop. The controller may receive a feedback signal representative of the output and vary one or more parameters of the switch in response to the feedback signal to regulate the output.
The energy transfer element in the power supply, sometimes called a transformer or a coupled inductor, is an inductive component with coils of wire (also referred to as windings) which are wound around a structure called a bobbin. The bobbin provides support for the coils of wire and also provides an area for a core of magnetically active material (such as ferrite or steel) to be inserted so that the windings can encircle the core. The area around the bobbin where the windings can be wound is often referred to as the bobbin window.
During operation, the energy transfer element allows for the transfer of energy between an input side (also referred to as a primary side) of the power converter and an output side (also referred to as a secondary side) of the power converter. A winding utilized for power conversion is generally referred to as a power winding. In addition, the energy transfer element may include additional windings that may not take part in the power conversion function. A winding that may provide both shielding functions and power conversion functions, such as, for example, a bias winding (also referred to as an auxiliary winding), which provides a bias voltage to operate a component of the controller, is generally considered a power winding. A power winding coupled to the input side of the power converter is generally called a primary winding (or input winding) while a power winding coupled to the output side is generally referred to as a secondary winding (or output winding). Additional windings, such as balance shield windings and cancellation shield windings, are sometimes included in the general category of shield windings to distinguish these windings from power windings that are used for the power converter to operate.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the various embodiments. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments.